Generally, a mobile terminal is adapted to make relatively infrequent measurements in an idle mode or on common channels and frequent measurements on dedicated channels. In the standards UTRAN (Universal Terrestrial Radio Access Network) and GPRS (General Packet Radio Service), frequent measurements on dedicated channels are only started on explicit order from the network. In said standards, broadcast information in an idle mode gives the mobile terminal information on a set of radio access technologies (RATs) and cells. In a connected mode the broadcasted set may be replaced by mobile-specific orders from the network.
There are several proposed solutions for managing radio resources in mobile communication systems, see e.g. WO02/032179 or EP0964595A2. Operators having several Radio Networks, such as GSM (Global System for Mobile communication) and WCDMA (Wideband Code Division Multiple Access) providing coverage in the same area, seek to control the traffic between the radio networks based on load and service. Typical objectives are optimization of the overall network capacity or optimization of the perceived performance (at least for selected services or user groups). To achieve this, users need to be moved between the available radio networks, in so called Intra Radio Access Technology Handovers (IRAT HOs), where so called Directed Retry is a special case, when handover is performed prior to allocation of a traffic channel.
One known solution for optimization of the overall network capacity or optimization of the perceived performance is setting up the requested service(s) in the current RAT, during service evaluating the potential candidate cells and, if a better candidate RAT/cell is found, moving the “call(s)” to a more suitable RAT/cell. This solution has the disadvantage that all services need to be designed in all RATs and packet switched protocols will perceive an interruption which is longer than minimum. Thus, the packet switched protocols will not reach their highest throughput.
Another known solution is to evaluate potential candidate RAT/cells already at the service request and, if the call should be allocated to another RAT/cell, immediately set up the call in the target RAT/cell. However, this has the drawback that accurate measurements on candidate RAT/cells may delay the call setup several seconds. If a short measurement period is used instead, there may be a significant risk that the assignment fails.
User equipment, such as mobile terminals, is known to base, in order to provide better accuracy, initial measurements at call setup on measurements made previously in an idle mode. Thereby, so called “smart re-use” of the previous measurements can be used, but nevertheless, the previous measurements are typically relatively inaccurate due to long sleep periods (DRX cycles).
In UTRAN, there is a possibility to utilize a so called compressed mode for service setups and connections, in order to increase the service capabilities of a network. However, there is often in UTRAN an upper limit for the compressed mode traffic fraction in a network node. Hence, it is undesirable to activate the compressed mode at all call setups. The consequence is that the compressed mode is activated only when the desired service is known, so that there is no decrease of the traffic load contribution of a service setup before the type of service requested is known by the network.
In order to reduce the interruption of initial signaling by measurements, it has been suggested to provide a separate measuring receiver in mobile terminals. However, this will make it larger and more complex, power consuming and expensive.